<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
  <script src="./rem.js"></script>
  <style>
    body {
      margin: 0;
    }

    header {
      height: .88rem;
      background: #333;
      color: #fff;
      line-height: .88rem;
      text-align: center;
      font-size: .2rem;
    }
    
  </style>
</head>
<body>
  <header>
    文字
  </header>
</body>
</html>